Abstract

This thesis investigates a range of novel photonic devices and their constituent semiconductor materials with emission in the infrared (IR) region of the spectrum. These have a variety of potential applications, including in telecoms, sensing and defence systems. Studies focus on aspects of the electronic and photonic band structures, and how these impact upon device performance.
Type-II interband cascade lasers and LEDs emitting in the mid-IR region of 3 – 4 μm are characterised using temperature and hydrostatic pressure dependent techniques. The key finding is that the threshold current density exhibits a minimum for emission around 0.35 eV (~3.5 μm), in both the pressure dependent results and data for many devices with different design wavelengths. The increase in threshold current density towards lower energies can be explained by an increase in CHCC Auger recombination. The increase in threshold current towards higher energies cannot be well explained by an Auger process, and it is concluded that this may be evidence of defect-related recombination.
Dilute bismide alloys are an interesting new material system for IR applications. The electronic and optical properties of several dilute bismide alloys are determined by spectroscopic ellipsometry. Key findings include the first experimental measurements of the spin-orbit splitting in GaNAsBi, which show that it is approximately independent of N content, and the first evidence for a decrease in the direct band gap of GaP with the addition of bismuth, reducing by 130 ± 20 meV/%Bi. The refractive index was determined for all the materials and in the transparency region the real part of the refractive index was found to decrease approximately linearly with increasing band gap.
In addition to modifying the electronic properties, photonic effects can be used to develop new IR devices. Finite difference time domain simulations of photonic crystal cavity structures within thick multi-layer slabs were carried out. These showed that it is possible to achieve high Q-factors, > 10^4, in slabs with refractive indices corresponding to typical semiconductor heterostructures. This opens up possibilities for designing photonic crystal lasers that do not require the thin suspended membranes typically found in the literature, with applications in integrated photonic circuits and on-chip sensors.